A switch unit, preferably implementing a circuit breaker, includes a contact slide unit formed by a contact slide, a fixed contact piece and a moveable contact piece), and a short-circuit release that acts to displace the moveable contact piece by means of a tappet in the event of a short-circuit. A moveable braking device is configured and arranged such that, following circuit opening displacement of the moveable contact piece in response to a short-circuit, the moveable brake device dampens the return, rebound movement of the moveable contact piece to reclose the circuit.